To realize the potential of cell-based therapy for treating injuries and degenerative diseases, renewable sources of stem/progenitor cells need to be developed. Although embryonic stem cells (ESCs) indefinitely self-renew and have the differentiation potential to become any cell type, in practice, they are inferior to lineage-restricted cells as they are prone to causing teratomas and do not repopulate host tissues in vivo. However, significant challenges also remain in terms of the isolation and long-term expansion of most tissue-specific stem/progenitor cells from adults (e.g., even for the arguably most studied hematopoietic stem cells). Consequently, differentiation of ESCs into (e.g. hESCs) renewable tissue-specific cell types is highly desirable for various biomedical applications. If achieved, cell populations could be carefully quality controlled and serve as starting materials, omitting the need to use ESCs (e.g. hESCs) that cannot be used directly. Furthermore, despite significant advances in development of various neural induction conditions for ESCs (e.g. hESCs), most differentiation protocols use poorly defined culture conditions (e.g., going through embryonic bodies (EB) formation, using undefined medium supplements such as knockout serum replacement (KSR)), and usually yield mixed populations containing neural cells at different developmental stages, or even other embryonic germ layer lineages and undifferentiated hESCs.
In response to the need, we developed methods and robust chemically defined media conditions involving specific small molecules that rapidly and uniformly convert ESC or inducible pluripotent stem cells into neural stem cells (NSCs), which importantly, enable long-term expansion of NSCs without a loss of high neurogenic propensity and regionalizable plasticity. To our knowledge, we provide the fastest and most efficient method so far to produce neural stem cells from embryonic stem cells (ESCs). In addition, NSCs differ from previously reported hESC-derived NSCs in that they represent the primitive pre-rosette neuroepithelium that has never before been expanded in vitro long-term.